I. Technical Field
The present invention relates to a rocker arm of an internal-combustion engine.
II. Description of the Related Art
Traditional rocker arms utilized in valve trains of internal consumption engines are generally manufactured as forgings or casts. However, as revolution and output power of the internal consumption engines have increased in recent years, there has been an increasing desire for inertial-weight saving. Accordingly, arts for manufacturing the rocker arms by plastic working (such as press working) have been proposed for the purpose of weight saving. One of such art is disclosed in Japanese Unexamined Patent Application Publication No. 2007-056690.
However, it is difficult to perform drilling with high accuracy for the rocker arms manufactured by press working. Therefore, while each cam follower has a portion on a surface thereof that makes sliding contact with each cam (this portion of the surface of the cam follower will be hereinafter be referred to simply as “the slide-contact surface of the cam follower”), it has been assumed that it is difficult to realize any oil passage for supplying lubricant to the slide-contact surface of the cam follower. Therefore, according to proposed methods, supply of lubricant to such rocker arms has been not through the rocker arms themselves but through other paths (such as what is usually referred to as shower flow) outside the rocker arms.
However, mounting of the other paths such as the shower flow has problems such as increase in internal volume and in weight of the internal consumption engines along with mounting of the other paths. On the other hand, the inventors of the present invention found that, since lubricant supply from the other path is farther in comparison with lubricant supply from the rocker arm onto itself, it is difficult to efficiently supply lubricant to the slide-contact surface of the cam follower. This is not limited to the rocker arms manufactured by press working. V-engines, which have been spreading recent years, brought increase in number of camshafts and valves, which then brought increase in load that the camshafts bear. Along with this, there has been an increasing desire for higher efficiency in lubricant supply.
Thus, there is a need in the art for a rocker arm that can improve the efficiency of supplying lubricant to the slide-contact surface of the cam follower.